1. Field of the Invention
The present invention relates to a fiber reinforced cement board using as a raw material a hydraulic inorganic material such as cement and a manufacturing process thereof.
2. Description of the Related Art
Hitherto, fiber reinforced cement boards are generally fastened by nailing.
For example, a first fiber reinforced cement board placed downward is nailed to a sheathing at the points about 20 mm below the upper edge of the first board.
Then, the lower part of a second fiber reinforced cement board to be placed above the first board is placed on the upper part of the first board so that the front side of the upper part of the first board faces the backside of the lower part of the second board, and the second board is nailed to the sheathing at the points about 20 mm below the upper edge of the second board.
Such laminating installation method is referred to as lap boarding installation method.
Such fastening by nailing may cause breakdown, fracture or cracking of fiber reinforced cement boards when these boards are too rigid.
In order to overcome such problem, there have been discussed various reinforced boards such as the boards in which the specific gravity thereof is decreased by addition of a lightweight material to facilitate nailing.
For example, U.S. Pat. No. 6,572,697 discloses decreasing a specific gravity to 1.2 g/cm3 or less by adding volcanic ashes; Kokai publication JP 2000-264701 gazette discloses addition of wood fibers having a specific length and a specific width as a reinforcing material; Japanese Patent Gazette No. 2730835 discloses addition of pulp fibers which have been divided to a specific size and synthetic resin fibers having a specific length as reinforcing materials; and Japanese Patent Gazette No. 2619908 discloses addition of pulp fibers and fibrillated hemp fibers as reinforcing materials.
However, addition of an excess amount of the above-mentioned woody reinforcement naturally leads to poor fire-resistance and extreme decrease of the specific gravity may lead to decrease in various physical properties other than nail performance, such as bending strength.